Variable transformer for alternating current welders



Sept. 1, 1953 F, M L 2,651,023

VARIABLE TRANSFORMER FOR ALTERNATING CURRENT WELDERS Original Filed June 13, 1946 2 Sheets-Sheet l INVENTUR F'RHNEIE E:- MILLER HTTDRNEPS p 1953 F. B. MILLER 2,651,023

VARIABLE TRANSFORMER FOR ALTERNATING CURRENT WELDERS Original Filed June 13, 1946 2 Sheets-Sheet 2 war E I 5 L1 -14- a, L4 n K 55 L "12,14 T L5 3 G8 L-24 I L4 g Y 1mllllllnmhmuf fie Mariam E'ITURNEHS Patented Sept. 1, 1953 VARIABLE TRANSFORMER FOR ALTERNAT- ING CURRENT WELDERS Francis B. Miller, Dayton, Ohio, assignor to The Commonwealth Engineering Company of Ohio, Dayton, Ohio, a corporation of Ohio Original application June 13, 1946, Serial No. 676,407. Divided and this application May 15, 1951, Serial No. 227,261

3 Claims.

This invention relates to welding apparatus and to methods of welding and in particular to methods and apparatus for electric arc welding.

This application is a division of Francis B. Miller application, Serial No. 676,407, filed June 13, 1946, now Patent No. 2,577,258.

The object of this invention is to provide an improved alternating current are welder having a more stable arc than has heretofore been possible.

It is another object to provide an alternating current arc welding transformer which tends to maintain a stable are by imposing a high voltage across the arc when the welding current drops to zero.

It is still another object to provide a welding transformer according to the foregoing objects which employs a multi-phase input circuit for a single phase output circuit.

It is still another object to provide a welding transformer having quick recovery characteristics and which is variable in output.

It is still another object to provide a welding transformer havng the above mentioned characteristics and which employs the principle of the auto-transformer for obtaining these characteristics.

Another object is to provide a method of transforming multi-phase current into single phase by transforming one of the input phases directly and storing the power input of the other phases to be applied in synchronism with the said one phase for producing an integrated single phase output.

Another object is to provide transformers according to the foregoing objects which include a compensating winding for reducing the impedance of the circuits whereby large short circuit currents will flow for producing the high voltage required for the quick recovery of the secondary circuit following a short circuit.

These and other objects and advantages will become more apparent upon reference to the following description taken in connection with the attached drawings in which:

Figure 1 is a circuit diagram of a welding transformer for transforming three phase into single phase;

Figure 2 is a view showing a rectifier and power storage means which may be utilized in the circuit of Figure 1;

Figure 3 illustrates one form of relay which may be utilized in the circuit of Figurel;

Figure 4 illustrates a portion of the circuit of Figure 1;

Figure 5 is a View showing a modified arrangement of the circuit of Figure 1;

Figure 6 is a perspective view, partly in section, showing one arrangement of the transformers of Figures 1 and 5;

Figure 7 is a view illustrating an auto-transformer type of welding transformer adapted for practicing this invention;

Figure 8 is a view illustrating the physical arrangement of a transformer constructed according to the diagram of Figure '7; and

Figure 9 is a circuiting diagram of still another welding transformer according to this invention.

Referring to the drawings, and in particular Figure 1, the primary leads are indicated at Ll, L2 and L3 and may form a three phase circuit which can be, for example, at 220 volts and at a frequency of cycles per second.

The leads LI and L2 form a phase a which is connected to the terminals of a primary coil at In which is arranged in magnetic association with the transformer core [2.

The secondary of the transformer is indicated at M and has its terminals connected with the output terminals at L4 and L5. The voltage applied to the output terminals preferably ranges from to volts downwardly according to the particular work to be welded.

The lines L! and L3 form a phase b which is connected by a pair of wires IE to a rectifier and filter at IS. The output from the filter I8 is conducted through a variable resistor 20 to one terminal of a pair of coils 22 and 24, the other terminals of which are connected to one side of a relay 26. The other side of the relay 26 is connected to the other output terminal of the filter I8.

The relay 26 may be of any of several wellknown types and is connected by a pair of wires 28 with the phase a to be operated into its closed position in accordance with predetermined electrical conditions in phase a.

The coil 22 is associated with the transformer core i2 in such a manner that the lines of magnetic flux established by the said coil will add to those established by the coil 10.

The lines L2 and L3 form the phase c which is connected by the wires 30 with a second filter unit 32. The filter unit is, in turn, connected through a resistor 34 and a relay 36 with the coils 38 and 40 which correspond, respectively, with the coils 22 and 24. The relay 36 is, like the relay 26, operated from phase a by the wires 42.

The coils 24 and it are wound together with a coil 44 in the secondary circuit on a core 46. The coils are wound additively and thus form a high intensity choke, the principal function of which is toprovide for the quick recovery of the secondary voltage following the breaking of 'a secondary short circuit.

In Figure 2 there is illustrated a typical filter which may be employed at it! and 32 and which comprises the chokes 48 and the condensers 50 arranged in the usual manner. The condenser-"50 adjacent the output terminals of thefilter stores a predetermined charge whichis'delivered-to one of the coils 22, 38 when. the associatedr'irel-ay is operated. By providing filters having different delay characteristics, it is possible to store. power from a plurality of phases and thereafter to apply the same in phase with a master phase to the primary of a transformer, all of the phases adding to the primary flux in the transformer core.

Figure 3 illustrates one form of relay which may be employed at-Zii or 3:6 and comprises a pair of electronic tubes 52' .and 5.13 which are adapted for passing current in respectively opposite directions. The tube 52 may lee-triggered by the grid 53' thereof while the tube '54 maybe triggeredby the; grid 55- from the phase a in accordance with any predetermined voltage. The charge stored on the associated. condenser 58 is thus applied to the associated coil 22,33 in the proper direction and-time relationship to add to the coil Hi.

There is illustrated in Figure 4 one arrangement that the coils 2d, Ml and 44 and the core 46' may take. It will be seen thatthisportion of the circuit consists of .a multi coil iron core choke.

In Figure 5 there is shown an arrangement similar to that of Figure '1 in which similar parts are identified by the same numeral with an addi tion of a subscript a except for the input and output leads and the primary phases.

In Figure 5 the filters ind-and 32aare adapted for being connected to their respective transformer coils 2 2a and 3811 by the relays zta; and 36a respectively. The relays are operated by .a current relay .5 8 connected in one of the output leads so that the relays 26a and 136d are operated at or near the point where the secondary current passes through zero.

The circuit of Figure 5 also includes a compensatingcoil at 58 which is magnetically linked with a secondary coil Ma insuch-a manneras to reduce its impedance. The secondary circuit may also include the chokev shown in-the secondary circuitof Figure 1 as desired.

Both of the transformers of Figures 1 and 5;, are of the low leakage reactance or closely coupled type. Transformers-ofthis type have high short circuit current characteristics andarethus adapted for the maintenance of a stable .arc. Also, with high short circuit currents, the energy stored in the choke is high and, when the short is interrupted. a high are restoring voltage is applied to the output terminals.

During welding an arc is struck between the workpiece and the welding rod by touching the two together and the arcis thereafter maintained with the rod andworkpiece spaced apart.

As welding continues. the rod melts and drops thereof pass across the arc space and fuse with the metal of the workpiece. It has been found that the drops so passed. tend to stretch out tobridge the gap between the rod. and the workpiece and thereby place a short circuit on the- "up from. a: sheet.

, recovery voltage.

the secondary assists in quickly reestablishing the arc. characteristics result.

Thus, very stable and improved arc In Figure 6 there is illustrated one method of building a transformer according to the circuits of Figures-.1 and fi;

In this view there is a core at 60 which is preferably of a good grade of transformer lamination steel and may be rolled Arranged around the core 60 is .theprimary 'coi-l It, the secondary coil 14 and the auxiliary saturating coils 22 and 38. Arranged. around the coils is a shell 52 which is also preferably formed from a strip of high grade transformer steel. The core iii andv shell 5-2 are magnetically connected and structurally supported by the upper cast yoke {ill and the lower cast foot 66. Bolts 69 may be provided for clamping the entire assembly rigidly together.

.InFigure .7 there is shown the auto-transformer type wherein the primary leads. Li and L2 are connected with the oppositeends of a primary coil 68. The coil 68 is variably coupled on a core it with a secondary l2, one end of which is-connected with the lead Ll.

Rigidlymagnetically coupled in maximum inductive relation with. the secondary 12 is a short circuited compensating winding 1.4- which is-.for the purpose of reducing the impedance of the secondary l2. Since-thecompensating wind ing M- is permanentlycoup'led in a maximuminductive relation to secondary 72, it will at all times act to reduce the impedance inthe. secondary. Thus, regardless of the variation in input voltage, the. compensating winding M will always act vtoproduce the desired high short circuit current.

The other terminal .of the secondary i2 is connected with the. output terminal L4 while the other output terminal L5 is connected. with. the primary lead L2.

By varying thecoupling. of coils l2 and 68 the output voltage and. current may be variedv within a widerange and the output will have the characteristics provided for in this invention. .That is; a high .short circuitcurrent and .a quick recovery of welding voltage following. av short circuit.

The: physical arrangementof the circuit shown in Figurev '1 is. illustrated in. Figure 8 wherein. the primary 68=is wound on one leg of a core 76 which is-apertured-in one-of the other legs for receiving acylindrical magnetic member 18. The member It has wound on one side thereof a coil 12 and on. the other sidethereofa coil M. By rotating the member 18, thecoupling between the coils l2 and 68' may be varied.

As in the case of the transformers shown on Figures 1 and 5,. the transformer of Figures '7 and 8 is closely coupled, having low leakage re actance. ahigh short circuit currentand a relatively high Also, becauseof the close coupling the power factors at which these trans formersoperate is exceptionally high.

Of particular advantage in many instances is thearrangement of this invention whereby a plurality of phases are employed to produce a single Thus, in each case the transformer hasphase. By thus dividing the welding load over several phases, no one phase is overloaded, smaller wiring may be used, and fewer precautions need be taken to maintain the proper line voltage in other parts of the primary circuit.

In Figure 9 there is shown a first transformer at 80 having a primary 82 supplied from the power lines LI and L2 and a secondary 84 whose opposite ends are connected with the output terminals L4 and L5.

serially connected with the secondary 84 is an iron core choke 86 and a secondary 88 of a second transformer 90. The secondary B8 is variably energized from the primary 92 of the transformer which is connected with an adjustable source of power at 94 which consists of a regulator or variator having the coils 86 and 98 which are connected to receive power from the lines LI and L2.

In operation, the voltage supply of the coil 88 may be arranged to add to or to subtract from the voltage of the coil 84 to vary the voltampere characteristics of the output.

The transformers 80 and 90 are closely coupled so that high short circuit currents flow and thus there is a high recovery voltage available when the short circuit is eliminated. The choke at 86 contributes to the recovery voltage as well as the transformers.

It will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claims and the invention.

I claim:

1. An auto-transformer for welding comprising a coil having primary and secondary windings, said coil having opposite ends forming output terminals, said primary winding being connected with a primary supply circuit and being variably coupled with said secondary winding, and said secondary winding having permanently coupled in substantially maximum inductive relation therewith a short circuited compensating winding.

2. A welding transformer of the auto-transformer type having a secondary coil with its opposite ends connected with the output terminals of the transformer and divided into first and second windings, the opposite ends of said first winding forming the input terminals of the transformer, said first winding being variably magnetically coupled with said second winding; and a short oircuited compensating winding permanently magnetically coupled in substantially maximum inductive relation with said second winding.

3. In a transformer a magnetic core member comprising a pair of legs; a primary coil arranged on one of said legs for magnetizing said core; a cylindrical aperture in the other of said legs; a cylindrical magnetic member rotating in said aperture; a first coil on said cylindrical member, a second coil on said cylindrical memher in maximum inductive relation to said first coil, one of said coils being the transformer secondary and the other of said coils being short circuited to act as a compensating winding.

FRANCIS B. MILLER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,672,703 West June 5, 1928 1,701,774 Guerra Feb. 12, 1929 

